In the manufacture of transparent containers such as glass bottles and jugs, various types of anomalies can occur in the sidewalls, heels, bottoms, shoulders and/or necks of the containers. These anomalies, termed "commercial variations" in the art, can affect commercial acceptability of the containers. The commercial variations may be opaque such as stones or metallic particles, or may be refractive such as blisters, bubbles or tears.
It has heretofore been proposed to employ electro-optical inspection techniques for detecting commercial variations that affect optical properties of the containers. The basic principle is that a light source is positioned to direct light energy onto the container, and a camera is positioned to receive an image of the portion of the container illuminated by the light source. The light source may be of uniform intensity, or may be configured to have an intensity that varies across one dimension of the light source. Opaque and refractive commercial variations in the portion of the container illuminated by the light source are detected as a function of light intensity in the image of the illuminated container received and stored at the camera. U.S. Pat. Nos. 4,601,395 and 4,958,223, both assigned to the assignee hereof, are illustrative of this technology.
U.S. Pat. No. 5,233,186, also assigned to the assignee hereof, discloses an apparatus and method for detecting commercial variations in transparent containers that include a conveyor for directing containers along a path through an inspection station, and a light source disposed on one side of the path for directing light energy through a container at the inspection station. A light sensing camera is positioned on the same side of the conveyor path, and a reflector is positioned on the opposing side of the conveyor path opposite the light source and camera for reflecting light energy transmitted from the light source through the container at the station back through the container to the camera. A beam splitter is positioned between the light source and the camera to separate the illumination light energy from the reflected light energy. The camera includes an array sensor that is scanned at increments of container rotation for developing a two-dimensional electronic image of the container. Commercial variations are detected as a function of variations in intensity of light energy received at the camera, and consequent variations in the two-dimensional electronic image of the container.
Although the systems disclosed in the noted patents address problems theretofore extant in the art, further improvements remain desirable. For example, the disclosed systems are not well adapted for inspecting portions of containers having differing optical properties, such as large jugs having knurled bands at the top and bottom of the jug sidewalls to help prevent scratching and cracking as the jugs hit each other during normal use. Because of the knurling, these bands exhibit a refractive characteristic--i.e., normal refractive noise--as compared with the remainder of the sidewall, and thus appear as dark bands in the image of the container independent of any commercial variations in the bands. It is therefore a general object of the present invention to provide an apparatus and method for electro-optically inspecting glass containers having portions, including particularly sidewall portions, of differing optical properties.